Non-aqueous secondary batteries (hereinafter, also referred to simply as “secondary batteries”) such as lithium ion secondary batteries have characteristics such as compact size, light weight, high energy-density, and the ability to be repeatedly charged and discharged, and are used in a wide variety of applications. A non-aqueous secondary battery generally includes battery components such as a positive electrode, a negative electrode, and a separator that isolates the positive electrode and the negative electrode from one another and prevents short circuiting between the positive and negative electrodes.
Moreover, battery components including functional layers that impart desired performance (for example, heat resistance, strength, or the like) on these battery components are used in secondary batteries. Specific examples of such battery components include a separator obtained by forming a functional layer on a separator substrate and an electrode obtained by forming a functional layer on an electrode substrate formed from a current collector and an electrode mixed material layer provided thereon. Moreover, a functional layer composed of a porous membrane layer formed by binding non-conductive particles using a binder (binding material) is one example of a functional layer that can improve heat resistance, strength, or the like of a battery component. This functional layer can be formed, for example, by applying a composition for a functional layer that contains non-conductive particles, a binder, and a dispersion medium onto the surface of a substrate (for example, a separator substrate or an electrode substrate), and then drying the applied composition for a functional layer.
In recent years, much effort has been focused on enhancing compositions for non-aqueous secondary battery functional layers used in the formation of functional layers with the aim of further raising secondary battery performance (for example, refer to PTL 1).
In one specific example, PTL 1 proposes a technique for improving binding capacity and homogeneity of a functional layer through formation thereof using a composition for a functional layer that only contains a water-soluble polymer including a repeating unit derived from (meth)acrylamide and having a weight average molecular weight of 3×105 to 6×106 as a binder.